Vector parallel to the line of intersection of two planes, each spanned by two given vectors: angle with another vector

1. A.
   $\frac{3\pi}{4}$
2. B.
   $\frac{2\pi}{3}$
3. C.
   $\frac{4\pi}{5}$
4. D.
   $\frac{5\pi}{6}$

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1. A.
   $\left( \frac{\pi}{4},3\sqrt{6} \right)$
2. B.
   $\left( \frac{\pi}{3},3\sqrt{6} \right)$
3. C.
   $\left( \frac{\pi}{3},6 \right)$
4. D.
   $\left( \frac{\pi}{4},6 \right)$

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